Arterial oxygen tension and pulmonary ventilation in horses placed in the Anderson Sling suspension system after a period of lateral recumbency and anaesthetised with constant rate infusions of romifidine and ketamine.

Abstract

REASONS FOR PERFORMING STUDY: Some controversy exists over whether or not horses' recovery and cardiopulmonary function are affected by suspension in slings. OBJECTIVES: To measure arterial oxygen tension and pulmonary ventilation in anaesthetised horses placed in a standing position in an Anderson Sling (AS) after a period of right lateral recumbency (RLR). STUDY DESIGN: Randomised crossover experimental study. METHODS: Six Standardbred horses were anaesthetised twice. Catheters were inserted into the right jugular vein and the left carotid artery. After premedication with romifidine, anaesthesia was induced with diazepam and ketamine. Following 50 min in RLR, horses were maintained in either RLR or AS for an additional 60 min through to recovery. Anaesthesia was maintained i.v. with a constant rate infusion of romifidine and ketamine. Heart rate, respiratory rate, mean arterial pressure, expiratory tidal volume, minute volumes and end tidal CO2 were monitored continuously. Venous and arterial bloods were sampled for lactate concentration, creatine kinase activity and blood gas analysis before premedication, after induction, every 20 min for 100 min, as soon as the horse was standing (TR), and 24 h later. The data were averaged within 2 anaesthetic periods: P1, 0-20 min; and P2, 40-100 min. RESULTS: During P2, horses in the RLR group had lower arterial oxygen tension (P = 0.001), higher alveolar-arterial oxygen tension gradient (P = 0.005), higher respiratory rate (P = 0.04) and higher minute volumes (P = 0.04) than horses in the AS group. Arterial CO2 tension and mean arterial pressure increased in the AS group during P2 (P = 0.01 and 0.02 respectively). The recoveries were judged better in the AS group than in the RLR group (P = 0.01). During TR, lactate were higher in the RLR group than in the AS group (P = 0.007). Creatine kinase activities were higher in the AS group at 24 h vs. TR (P = 0.02). CONCLUSIONS: Anderson Sling suspension after a period of recumbency improves cardiopulmonary function and recovery quality in horses and therefore might be considered for use to recover hypoxic horses.